Good News, Bad News In Battle Against European Crab Invasion

There’s good news and bad from the battle against invasive European green crabs at the eastern end of Washington’s Strait of Juan de Fuca.

The good is that, the infestation appears to be pretty localized on Dungeness Spit, with the crustaceans only being found in an interior channel of Graveyard Spit.

LORENZ SOLLMAN OF THE U.S. FISH AND WILDLIFE SERVICE INSPECTS A TRAP SET OUT TO COLLECT INVASIVE EUROPEAN GREEN CRABS AT DUNGENESS NATIONAL WILDLIFE REFUGE EARLIER THIS YEAR. (ALLEN PLEUS, WDFW)

The bad is that the 76 trapped there to date far outnumber how many were found at two North Sound sites last year, “heightening the need for aggressive trapping and removal efforts to reduce the chance that the population could become a permanent fixture in the area.”

And it’s the breeding season and the crabs are less likely to crawl into traps.

So reports Emily Grason of the Washington Sea Grant Crab Team in an update posted this morning.

The worry here is what the green crabs could do to eelgrass pastures — so important for our salmonids and other fish — and clam beds, if they establish a sustaining population. Their arrival in Maine centuries ago is pinned on “dramatically” lower clam harvests and damage to kelp beds from their digging, and officials are concerned about what sort of impact they’ll have on shellfish and habitat here.

So, federal, state and tribal crews have been putting a lot of time and energy into trying to eradicate the unwanted crabs since their mid-April discovery at Dungeness National Wildlife Refuge, running more than 2,000 trap sets, and they’ve been learning more about the colony.

Earlier this spring, the theory was that larva had floated across the Straits from Sooke Bay on Vancouver Island, site of the first green crabs in the region, during the Blob-hot summer of 2015.

But now it’s believed they may have arrived last year because of their relatively small size, an inch to 2.5 inches across the backs.

“Based on how fast we know crabs grow, we can tell that this is a relatively new population, and likely arrived at Dungeness Spit during 2016,” Grason reports. “The wide range of sizes could reflect the fact that a female green crab can release multiple broods per year in Pacific Northwest, where our temperate climate allows a longer growing season for this species than is seen in other parts of the world.”

DNA testing will also help determine whether those at the spit are in fact related to the Sooke stock, coastal populations, or come from somewhere else.

With this being the start of the breeding season, crews are concerned that Dungeness could provide a jumping-off point for more populations to take hold in Puget Sound. Unfortunately, there are dozens upon dozens of locations from Orcas Island to Olympia that are highly or moderately suitable for green crabs.

A WASHINGTON SEA GRANT MAP SHOWS HIGHLY AND MODERATELY SUITABLE HABITATS FOR EUROPEAN GREEN CRABS. THEY’VE ONLY BEEN FOUND AT THREE LOCATIONS — WESTCOTT BAY ON SAN JUAN ISLAND, PADILLA BAY, AND DUNGENESS SPIT, SO FAR. (WSG)

But working fast and hard to get on top of this emerging problem could help slow or even stop the invasion in its tracks.

“Recent efforts in California have shown that very intensive, consistent trapping can have a dramatic impact on populations in isolated locations,” Grason notes. “At Graveyard Spit, the population seems, so far, to be small and isolated, easier to tackle than if green crab showed up everywhere all at once.

Ongoing trapping and monitoring is planned through the summer here, and crews are fanning out to test nearby habitats for green crabs.

Likening the situation to prevention of forest fires, Grason writes, “It’s difficult to forecast exactly where, when, or how severe they will be when they do pop up, and yet it’s imperative to respond quickly and aggressively as soon as they are detected, and while they are still small. Early detection is the foundation of this process, and here we are fortunate to have so many volunteers, partners, and beachgoers as our ‘lookouts’ for any smoldering green crab invasions.”

In a recent TVW video, WDFW’s Allen Pleus calls early detection the “second cheapest thing we can do.”

A bill funding the fight against aquatic invasive species has passed the Senate unanimously twice, but needs the House to agree and Governor Inslee to sign it.

As we’ve written here before, this is no time for lawmakers to get crabby about funding.

To learn how to spot green crabs and differentiate them from juvenile Dungies and red rocks, as well as find out more about the efforts of the Crab Team, go here.